This is a blog about the native conifers of the Pacific Northwest. It is a companion to the Northwest Conifers site. The blog will focus on timely and interesting details about our conifers, their connections to the rest of the environment, and our connection to them.

Monday, January 16, 2017

How Do Conifers Survive the Snow?

Snow is not friendly to trees, as we have seen, with the recent snow in the Portland area, which brought down limbs and entire trees. We see how destructive snow can be to trees, yet when we go to the mountains we see trees thriving there where the snow accumulates to many feet every winter. How is it that the trees in the mountains survive these mountains of snow?

First, we can notice that the trees growing in the mountains are not the same species as those we typically see growing in the lower elevations. Secondly, we have to remember that trees adapt to the environment that exists where they grow naturally. Several important adaptations have enabled conifers to survive deep snow without limb breakage. 

Conifers growing near the timberline show the most extreme adaptations to heavy snow. If you drive up to Timberline Lodge on Mt. Hood and look at the trees growing there, the first thing you might notice about them is that they grow as narrow spires with very short limbs. Other adaptations include drooping limbs that shed the snow and flexible limbs that bend without breaking when weighted down with snow.  

Subalpine Fir
Perhaps the most iconic of the conifers growing at the timberline is subalpine fir, which adopts the form of the Eiffel Tower. It is one of the more photogenic trees at the timberline, with tall spires pointing skyward. It avoids limb breakage by keeping its limbs close to itself. The short limbs don’t collect much snow on them, and the snow that does collect doesn’t get much branch-breaking leverage.

Pacific silver fir has slightly longer limbs, but they are pointed down where they can shed snow. Even when snow accumulates on the limbs, their orientation prevents breaking.

Pacific Silver Fir
Another strategy is to just bend under the burden of the snow. Mountain hemlock is fairly adept at this technique. It also tends to have shorter upper limbs than many other conifers. In the most extreme conditions, mountain hemlock has another trick: It stays low. At the highest elevations it grows as a low shrub. The weight of the snow can bend it to the ground, where it stays until the snow melts in the spring. This bendable habit also gives mountain hemlock an alternate way to reproduce. Limbs weighted down to the ground can take root. You can see patches of mountain hemlock growing near the timberline that reproduce in this way.

Whitebark pine is even more bendable than mountain hemlock. The branches of whitebark pine simply bend with the weight of the snow. In fact, its twigs are so bendable that you can tie one in a knot. That is one way to distinguish it from western white pine. Like mountain hemlock, whitebark pine branches can also take root when forced to the ground by snow.

Mountain Hemlock
Limber pine, which grows in the Wallowas and Rocky Mountains, is a close relative of whitebark pine. Limber pine is the king of bendability. Just in case you didn't know, its common name and scientific name (Pinus flexilis) both describe this feature. 

Conifers also benefit from the snow. Besides the obvious benefit of water from melted snow, the snow is a good insulator. It keeps the ground and roots from freezing in winter. Low-growing trees are also covered and protected from cold temperatures.


See also
How Do Conifers Survive the Cold?
Northwest Conifers: High-elevation Conifers
USFS: Mountain hemlock (Tsuga mertensiana)
USFS: Whitebark pine (Pinus albicaulis)

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